The use of organic molecules to modify the interface between metal and high-permittivity (K) material is a recent development that has a wealth of potential applications in microelectronics, optoelectronics and in the rapidly growing area of molecular electronics and bio-nanodevices. In terms of molecular control over electronic device properties, there have been two main approaches a) control of the electrical potential at the interface (electrostatics) and b) control of charge transport across the interface (electron dynamics). Relying on electrostatics instead of dynamics may be advantageous with respect to stability and reliability.
A GaAs sensor and Au—Si and Au—GaAs diodes have been demonstrated by incorporating molecules at such interfaces. In biological applications, SAMs have been primarily used as surface modifiers; the surface hydrophobicity and hydrophilicity is contingent on the type of SAM, which allows the control of biological host response such as biocompatibility and biodegradability. Another growing use of the SAM is activating a surface for subsequent chemical reaction, such immobilizing antibodies for biosensors.
In the future, the integration of high permittivity (K) gate dielectric films in complementary metal-oxide-semiconductor (CMOS) devices (i.e., field effect transistor or FET) will determine the minimum obtainable equivalent oxide thickness (EOT), as well as the drive performance, density and reliability. Soon, the deposition of gate metals on high K gate dielectrics (to completely eliminate EOTgate) will be needed. However, the work functions (φm) for n-MOSFETs (e.g. Al, Zr, Ti) and p-MOSFETs (e.g., Pt, Re, Ir) must precisely be controlled within Ec±0.2 eV and Ev±0.2 eV, where Ec and Ev are the conduction and valence band edge energies, respectively. This requirement arises because the flexibility in the control of low transistor threshold voltages (VT) is primarily offered by the control of the flat band voltages (VFB), which in turn are a function of the φm of various metals.
The production of such dual-metal MOSFETs will not only introduce additional process complexities (deposition/etching) and issues of yield, the potential for interfacial reactions of low electronegativity metals with high K dielectrics could lead to non-zero values of EOTgate, as well as a change in the effective φm of metals. Therefore, there needs to be an alternative solution to tuning specific metals. It also would be highly desirable to eliminate the use of dual metals in CMOS with high K dielectrics.